It's salty, powerfully savory, as unctuous as foie gras and as spreadable as softened butter.

Leave it to two Bay Area entrepreneurs with biology degrees from MIT and Harvard to transform bland tofu into an age-old, obscure Japanese specialty known as tofu misozuke or miso-cured tofu that they're now making and selling.

The couple, Oanh Nguyen, 30, and Dang Vu, 32 were vacationing in Japan a few years ago when they accidentally stumbled upon a brew pub that served the tofu. "We were blown away by how rich it was," Vu says. "I never thought tofu could taste like that."

That set off a 2-year quest to try to replicate it. They succeeded in coating firm tofu with sugar, sake and yellow miso, then aging it for two months.

Nguyen makes the misozuke tofu at a commercial kitchen in Belmont, when she isn't working as a manager of corporate strategy for Intuit in Mountain View. Vu lends a hand when he flies in regularly from Michigan, where he is finishing a Ph.D. program in cancer biology.

The cured tofu can be mixed into salad dressings, marinades or dips. Or served with crackers, cucumber slices or carrot sticks. Vegans can use it as a cheese substitute, and some Bay Area Japanese restaurants, including Ippuku in Berkeley, are incorporating it into their menus.

Rau Om tofu misozuke is $7 for a 2.5-ounce package at Rainbow Grocery in San Francisco, the Pasta Shop in Berkeley, New Leaf Community Markets, the Palo Alto California Avenue Sunday farmers' market, and online at rauom.com.